ORAL AiND APICAL SYSTEMS OF THE ECHINQDERMS. 375 



Fig. VIIL— Gastrulaof Co»2«^«/«. (After Wyville Thomson.) 1. Ter- 

 minal plate at the base of the stem. 3. Basal plates. or. Oral 

 plates. bl. Blastopore. 



and Pourtales* describes the root portion of the stem of 

 the recent Rhizocrinus Rawsonii as appearing to have 

 been " partly attached to a solid body by enlarged sur- 

 faces." 



On the other hand, in R. lofotensis and in Bathycrinus 

 the base of the stem is attached by radicular cirrhi, or by 

 strong-jointed branches that descend into the ooze on the 

 surface of which the animal lives, as was the case in some 

 Cyathocrmidcs. But it is of course not impossible that in 

 the larval condition, the stem may have had a terminal disc 

 of attachment, which was resorbed when the cirrhi appeared 

 and it became no longer necessary. 



The fact that the whole length of the stem intervenes 

 between its disc of attachment (figs, viii, ix, 1) and the 

 basal plates (figs, viii and ix, 3) is no argument against 

 my view that the former is homologous with the central 

 abactinal plate of a Starfish or Sea Urchin. A precisely 

 analogous case occurs in the Starfishes, in which the radials 

 do not remain in close contact with the genital plates as 

 in the Echinids, but are carried out of the apical system 

 altogether, to form the so-called ocular plates at the ends of 

 the arms, by the constant formation of new spines at their 

 bases. 



^ " On a New Species of Rhizocrinns from Barbadoes," ' Zoological Re^ 

 suits of the Hassler Expedition," p. 27, 



